QuantLib is a cross-platform, quantitative finance
C++ library for modeling, pricing, trading, and
risk management in real-life. It is also wrapped
as Python/Ruby/Scheme modules. Extensions for
Excel, R, and Mathematica are available. Other
such extensions are under consideration. QuantLib
offers tools that are useful both for practical
implementation and for advanced modeling. It
features market conventions, yield curve models,
solvers, PDEs, Monte Carlo (low-discrepancy
included), exotic options, VAR, and so on.

Ruby/Google offers a higher-level abstraction of Google's SOAP-driven Web API. It allows the user to programatically query the Google search engine from Ruby. The aim of the library is to shield the programmer from the details of the raw data structures returned by the Web API, and in the process make the API more accessible for everyday use.

RuStem is a fast Ruby module with the the Porter
stemming algorithm (a process for removing the
commoner morphological and inflexional endings
from words in English; its main use is as part of
a term normalisation process that is usually done
when setting up Information Retrieval systems).

Ruby/DICT is an RFC 2229-compliant client-side library implementation
of the DICT protocol, written in the Ruby programming language. It can
be used to write clients that access dictionary definitions from a set
of natural language dictionary databases. rdict, a powerful CLI
dictionary client built on Ruby/DICT, is included.

Ruby/Password is a set of useful methods for creating, verifying, and manipulating passwords. It includes an interface to CrackLib, a library commonly used for checking password strength. It is intended to be used by system administrators who need to write Ruby programs that prompt for, generate, verify, and encrypt passwords.

For Ruby developers, YAML is a natural fit for
object serialization and general data storage, as
their semantics are similiar. YAML4R is a
fully-featured YAML parser and emitter for Ruby.
Use it as a drop-in replacement for PStore, or use
one of its several APIs to store object data in
the friendly and readable YAML style.

Radiuslib is a complete RADIUS protocol and
utility library for the Ruby programming
language. It includes a very featureful, RFC-
compliant protocol implementation, as well as
parser classes for RADIUS dictionaries,
Cistron-format "users" files, and
standard "detail" accounting logs.